Jason's Firefly .46 Build

Yes 1 cut all the way through the others make it easier to expand and hold some grit.

MT taper should be OK

Some of the woodworking supplies sell the Silicon Carbide in small containers but the 1000g or 1200g is a bit harder to find but can be had on e-bay as it is used for stone tumblers but you will get enough to last several lifetimes

Also well worth a read of Ramon's thread here, the type of lap I used are described on page 5

Thank you Jason, superb,

The links are really interesting and I have found a source for 1000g on ebay.

Progress is slow at at the moment, I thought I was well equipped for this project but as I have no dedicated milling facility all that work has to be done off the vertical slide or the cross slide. I seem to making lots of parts to make parts? If that makes sense.

Will post some pics on this thread in due course but for now once again thank you for your reply.

geoff w

Jason,

Really appreciate the detailed build thread. I am planning for this to be my first IC motor so seeing your setup pictures is very helpful.

I am based in the States though and HE30 (6082) seems to be hard to come by. Curious if 6061 will be a viable substitute? I look forward to working on this over the coming holidays. The detailed plans and the fact that it can be made without any castings is very nice.

-Hash

Yes that should be OK, keep us posted of your progress.

J

Hi Jason and all,

Returned to the firefly recently, a photo of some of the parts in the previous post. (posted before I added text, doh!!!)

The silencer in the photo is off an SC engine and has centre fixing hole spacings at 37mm.

The whittaker drawings show 35.5mm. spacing for the silencer bolt holes. I assume this is to accommodate an OS silencer which has hole spacings at 1.38" (35mm.) If so that seems odd, why 35.5 why not 35?

I am tempted to use the SC silencer and adjust the hole spacings in the barrel to suit although this would of course preclude the use of an OS exhaust at a later date.

Justengines online have wide range of silencers at reasonable prices and varying hole spaces including 35 and 37 mm. Has anybody bought a silencer from them?

Reading online there seem to a variety of different silencers. Silent, extra silent? I would be interested in any opinions on silencers particularly ones suitable for the firefly.

Posted the photo again here. I have shortened the barrel and modified the liner to accept a removable aero sleeve. The head has also been modified as can be seen in the photo.

thanks to all geoff

Justengines are a reputable company, I've bought from them in the past, including silencers....

As for silent and extra silent, these were borne out of the need for models to be quietened down at noise sensitive sites....complaints from locals to the EA....and even though there were occasions when the sound levels were below the 82db threshhold, folk fitted quieter silencers anyway....this provided a niche market...

Edited By John Rudd on 06/12/2016 10:17:57

I'd be temnpted to see if those holes in your sliencer could be elongated slightly so they will fit the 35.5mm hole ctrs, might just need to turn down the screw head dia slightly if they touch the manifold.

I have also used Just engines a few times though not for silencers and they were fine to deal with.

John, Jason,

thanks for your replies, as ever always appreciated.

I think I will buy a 35 mm. silencer from Just engines, they seem like good value.

I don't want to modify the SC box as I may wish to use it again on the SC.

Really enjoying this project, much of the stuff I make requires very little precision.

This engine has been a real challenge. Can't see an a completion soon, sometime in early the new year, hopefully!!!

thanks again geoff w

Hi Jason, John and all

More questions if I may.

The piston design has a blind hole for the gudgeon pin. Is there any reason why?

My view, albeit from limited experience, is that if you drill and ream (5mm) right through for the pin you will accurately size the hole for a 5mm silver steel pin. The pin could then have a bronze cap at both ends.

I assume the cap is to protect the liner in the event of the pin sliding laterally in the hole.

Why does the cap have a hole down the centre?

Best to all Geoff

I've done them both ways so no problem if you wanted to do a through hole and caps both ends. There is also another vartation where you don't run teh reamer right through which allows the pin to be pushed into the hole and held by the taper left by the reamer. Some engines have the blind hole if the pin is likely to pass over a port in the cylinder liner as you don't want the pin snagging.

I've also done solid and drilled caps, think the reason for the hole is that any air trapped within teh pin at assembly could expand as the engine gets not and push the pins against the liner

Thanks Jason, good information.

Just the piston and con rod to make then lapping and fitting, lots to do but I think the finish may well be in sight.

I finished the crankshaft today drilling the hole for the crank pin.

I read your blog build notes first, glad I did, a 5.5 hole is a good press fit for 7/32" silver steel.

Photos show set up for drilling the crank pin hole using toolmakers button

atb geoff

Hi Jason/John and all,

I've had a long break from my firefly but started work on it again this week.

Lapped the liner, made the piston and lapped it into the liner. Just the gudgeon pin and the conrod to make and I can commence assembly.

Gudgeon pin is easy enough but a question if I may about the conrod.

The centre line of the crank pin boss, side view and the centre line of the waist, also from the side view lie on the centre line of the liner. Correct?

The gudgeon pin boss is offset, more on one side of this centre line than the other. Why is that?

Also which side of the gudgeon pin boss faces the front of the engine?

Best Geoff w

It allows for a thicker crank web. Being thicker the rod is further back so the offset is used to centralise the rod in the piston.

Thicker end to the front of the engine

Thanks Jason.

Just measured again, the following from my previous post is inncorrect

The centre line of the crank pin boss, side view and the centre line of the waist, also from the side view lie on the centre line of the liner. Correct?------ No INNCORRECT

The centre line of the crank pin boss is in fact offset from the centre line of the liner by 0.7 mm to the rear of the engine which accounts for the offset off the upper boss.

I'm glad I asked that question the answer has been most helpful.

First crap weather day we get next I'll make a start on it.

Not tomorrow though sunshine all day a spin up the M6 and a day Blackpool.

I have more questions but will leave them till next week.

Thanks you very much geoff

Hi Jason

I have decided if possible to not make the needle valve assembly and buy one instead.

I have found this one on ebay but not sure if it has the recommended needle os24081970.

Is the right needle important, would this assembly do the job

regards geoff

http://www.ebay.co.uk/itm/OS-Engine-Needle-Valve-Unit-Assy-40-46-65LA-26582900-/262770588512

Should do the job

Thanks

Hi Jason,

Firefly is all finished and assembled.

Once again, many thanks for your help and a superb build thread.

Pictures below. I have modified it a little with a shorter barrel and a removable aero sleeve and slimmer head. The head is slightly larger in diameter to accommodate wider hole spacings for the head bolts. This was necessary to ensure that the threaded holes in the barrel did not foul the transfer ports. The crankcase has deep groove ball bearings front (8) and (12) rear and the crankshaft has a conventional keyed drive for the prop driver.

Just a show pony at the moment, have not run it yet, that's another story.

A few final questions please. Was/is there any final consensus on the type of plug, prop, fuel etc. which is good for this engine. I have never started one before so I am now on another learning curve. big T again Geoff

Looks good.

Assuming you are just going to run it for the satisfaction rather than need any performance then any glow fuel will do, you don't need a high nitro content so 0-5% nitro would be more than adequate. Run it on the rich side to start with until things bed in.

I went with teh OS No 8 plug which is a good all rounder and a 10" dia x 7" pitch prop.